Alan Turing (1912-1954) was a seminal figure in the history of Western thought; he made significant contributions to the theory of logic, developed the foundations of the digital computer, cracked German war codes to save Britain, and promoted the idea of artificial intelligence before most scientists knew what a computer was.

In 1935, while still a student, working in the field of mathematical logic, Turing proposed an abstract computing machine which would became known as a "Turing Machine."

The Turing machine is simple in abstract: given an infinite tape, a scanner that could read, write, and erase symbols on the tape, Turing proved, you can solve any mathematical problem.

Any modern computer is essentially a modified Turing machine. The question at the center of artificial intelligence is: "Are human beings also Turing machines?" Or, put more simply, "could machines

simulate human behavior?"

For Turing, the answer to at least the second question

(and probably the first) was "yes," and, following a brief furlough where he cracked some of the most difficult German codes and likely won the war for Britain, he wrote a paper outlining a plan by which a Turing machine might be made to seem intelligent.

The article "Computing Machinery and Intelligence," in the 1950 issue of the philosophical journal Mind, took his work on computing machines as a base from which to ask the question "can a machine think?"

His answer was that if the responses from the computer were indistinguishable from that of a human, the computer could be said to be thinking. This is a very behavioristic model of intelligence; to Turing, the mind of the computer is a black box which receives input and produces output. It must have, he felt, a mechanism for learning from input and having its output corrected; by repeated give-and-take sessions where the machine would be presented with stimulus in the form of text, and produce a response in kind, it might learn to be intelligent. Due to this suggestion, and because of the wealth of ideas in his other work, Alan Turing is considered a principal founder of the field of artificial intelligence.